Field of the Invention
The invention relates to a device and a method for transferring flowable printing substances, in particular flowable printing inks, onto a printing material.
Description of Related Art
Printing methods exist, in which liquid printing ink is transferred onto a printing material by contact between a printing plate and said material. In these known methods the patterns to be printed are provided on the printing plate. The patterns may be provided on a surface as depressions and raised parts. Printing ink is applied on the raised parts (relief printing) or pressed into the depressions (gravure printing) and is transferred onto the printing material by contact with the printing material. The methods mentioned have the disadvantage that every new pattern to be printed requires a new printing plate.
From EP 1154905 a printing method is known for printing on printing materials with printing inks, in which different patterns can be printed using only a single printing plate.
For this purpose, a printing plate is used whose surface is formed with a raster of small openings with adjoining cavities. The small openings form the raster dots from which a pattern to be printed can be built. In a variant of the known printing method, the printing ink is sucked through the openings into the cavities by means of a vacuum in the cavities. An overpressure is generated thereafter in selected cavities, whereby the printing ink is applied onto the printing material through the openings of the respective cavities. The known printing method may also provide that printing ink is sucked only into selected cavities.
The known printing method is relatively complicated, since on the one hand the printing ink must not enter into the opening of the printing plate by itself, and on the other hand, however, the pressure difference generated in the cavity, which is caused for example by heating and cooling the gas filling in the cavity, must be sufficient to draw printing inks into the openings. This can only be achieved if the surface properties of the printing plate and the printing ink are exactly matched to each other. In addition, the process of generating a vacuum in a cavity and of covering the associated opening with printing ink must be synchronized very precisely with respect to time. These requirements make this printing method prone to failure.